This disclosure relates to logarithmic detector circuits and, in particular, to low noise logarithmic detector circuits.
A received signal strength indication (RSSI) circuit typically includes a logarithmic detector to provide an output that is a logarithm of the received signal amplitude. A single logarithmic detector circuit can be used; however, such a circuit may not be accurate over a desired dynamic range.
To compensate, the RSSI circuit can include tap points from multiple amplifier stages amplifying the received signal. The signals at the tap points are fed to logarithmic detectors, with each logarithmic detector receiving a larger signal than the last. The outputs of the logarithmic detectors are combined together into the output signal. As a result, the accurate range of an individual detector can be overlapped with the other detectors, providing an increased dynamic range over which the RSSI circuit has an accurate logarithmic output.
Unfortunately, in order to achieve the accurate performance over the wide dynamic range, multiple detectors and multiple amplifier stages are required. As the number of components increase, so does the noise of the RSSI circuit.
Accordingly, there remains a need for a low noise logarithmic detector circuit with accurate logarithmic output and adequate dynamic range.